1. Field of the Invention
This invention relates to apparatus and method for locating the center axis of the largest solid of rotation contained within an irregular elongated object. Although the method and apparatus may be used with any such elongated object, they may be employed to particular advantage in the wood products industry for aligning veneer blocks for peeling on a lathe into veneer. Accordingly, for the sake of clarity and to facilitate explanation of the invention, the method and apparatus will be described herein with respect to determining the center axis of the largest solid cylinder of wood contained within a veneer block. The veneer block can then be chucked in a veneer peeling lathe along this axis to recover the maximum amount of continuous sheet veneer that can be peeled therefrom.
In many conventional veneer plants, logs are brought to the mill and cut into segments called veneer logs or veneer blocks which are of a sufficient length to produce the desired width of veneer. Most frequently the veneer blocks are cut to lengths of either four or eight feet. These blocks are then introduced into the mill where they are treated to prepare them for peeling into veneer and are transferred by conveyors into the mill.
In some installations, the veneer blocks are loaded by the conveyors into vee blocks for approximate geometric centering. The vee blocks comprise two pairs of vees, each pair of which has an upper and lower v-shaped member which are hydraulically or mechanically interconnected to move in unison toward or away from one another. These blocks are always aligned to close on the clamping axis of the charger. The two pairs of vees close on the log until they can move no farther. The log is then clamped by the charger, transferred to the veneer lathe, and spindled in the lathe along the geometric center axis. As the veneer block is rotated in the lathe, a peeling blade is brought against the surface of the block and cuts the block into veneer.
This method of loading veneer blocks has the advantage that it is extremely rapid and thus the total volume of veneer produced in a given period is relatively high. The operator, however, is given no discretion in selection of the spin axis about which the log is rotated.
Other methods of loading veneer blocks give the operator control of the positioning of the veneer block in the lathe and thus permits him to account for irregularities and defects in the log, but these methods generally slow the veneer production process or require additional personnel. Moreover, these methods often give the operator little guidance in determining how to center logs which are not straight or which have non-circular cross-sections.
2. Description of the Prior Art
As the supply of available timber has decreased, the cost of such timber to sawmills and veneer plants has increased dramatically. Accordingly, for both environmental and economic reasons, numerous methods and devices have been invented and developed in recent years to improve the accuracy of positioning of veneer blocks and logs in the log processing apparatus in order to improve yields and eliminate waste.
For example, U.S. Pat. Nos. 3,504,719 to Don and 3,664,395 to Reed disclose two devices which perform mechanical centering of veneer blocks at two cross-sections along their length. These devices perform the centering very quickly, but do not account for curvature or bending of the log known as sweep and crook. U.S. Pat. No. 3,037,538 to Graham also discloses a centering device for veneer in which concentric rings of light are projected onto the ends of the log, and the operator shifts each end of the log until the circle of maximum diameter which will fit on each log end is determined. The centers of these circles are deemed to define the desired axis of rotation of the veneer block in the lathe. Although the operator presumably could make corrections for crook, sweep and off-center flaring, this apparatus provides no quantitative method for so doing.
U.S. Pat. Nos. 3,760,855 and 3,891,016, both to Nilberg, disclose an electro-mechanical apparatus which senses the surface of the log with a plurality of probes and determines the largest cylinder or stepped cylinder which fits within a mechanical model of the log. These devices, unfortunately, are quite complex.
U.S. Pat. Nos. 3,736,968 to Mason et al. and 3,746,065 to Mason disclose apparatus for determining the center axis of a log or veneer block. These devices employ photoelectric scanners and reorient the log or block with its center axis parallel to an index line of the processing equipment.
U.S. Pat. No. 3,857,579 to Sohn et al. discloses a device which is similar to Nilberg in that it determines the contour of the log surface at a plurality of cross-section locations along its length and locates the center axis of the largest cylinder which fits within the log cross-sections. This is accomplished by means of laser ranging devices which measure the surface of the log while the log is rotated. U.S. Pat. No. 3,945,125 to Mouat et al. similarly discloses an apparatus which measures the profile of the log while it is rotated in order to find the largest cylinder contained therein, but uses a mechanical probe in lieu of the laser ranging device of Sohn et al.
U.S. Pat. No. 3,749,499 to Reichard et al. discloses an optical masking techique used in the semiconductor industry for locating the center axis of the largest solid cylinder of semiconductor material contained within an elongated irregular rod of the material.